TABLE II.-Determination of the solubility of the precipitate of an official acid extract of soil in nitric acid.

The solubility of potassium phosphomolybdate in sodium nitrate solutions under different conditions was also investigated. A weighed quantity of the potassium phosphomolybdate was transferred to a gooch and 250 cc of sodium nitrate wash were run through as in analysis. The precipitate remaining in the gooch was then titrated with potassium hydroxid solution, 1 cc of the alkali used being equivalent to 0.0298 gram potassium phosphomolybdate. TABLE III.—Solubility of potassium phosphomolybdate in sodium nitrate.

A negative result for solubility was thus obtained, probably due to a small error in the factor previously obtained. It is evident that a sodium nitrate wash of 2 per cent strength exerts very little solvent action on the precipitate of potassium phosphomolybdate under the conditions of the experiment. On long contact, however, a marked solvent action is evidenced by the yellow color which a solution develops when in contact with the precipitate. A test of a saturated solution gave results close to those noted by Fraps (1905).

It was also noted that pure water decomposes the precipitate, as stated by Donk, with the separation of a whitish acid substance, supposedly molybdic acid. In our hands a solution of sodium nitrate of the strength adopted (5:1,000) gave also a slight turbidity when left in contact with the precipitate for a short time. A solution of sodium nitrate (10: 1,000) remains clear, however, under these conditions.

The preparation of the phosphomolybdic solution was also investigated, as it was noted that some solutions left no trace of insoluble residue when evaporated and taken up with nitric acid wash, while others left molybdic acid residues on evaporating, which required from 0.2 cc to 3 cc of standard potassium hydroxid solution to neutralize and which had to be allowed for as a "blank." Crystals of phosphomolybdic acid as furnished by Kahlbaum left no residue when the water solution was evaporated on a water bath and the dry residue again taken up with water. The nitric acid solution of the crystals, as recommended by Donk, when fresh left no residue under these conditions, but when allowed to stand some weeks left a residue from the nitric wash, which gradually increased in amount as the solution became older. The addition of a small amount of calcium and magnesium nitrate in the presence of a large excess of nitric acid seemed to prevent this, probably due to the formation of

soluble molybdates of calcium and magnesium with the separated molybdic acid. The presence of hydrochloric acid also prevented the formation of an insoluble residue, the hydrochloric acid combining with the molybdenum trioxid and forming a compound soluble in water or dilute nitric acid.

Phosphomolybdic acid solutions were prepared as follows:

100 grams phosphomolybdic acid. I.250 cc nitric acid (1.40 sp. gr.).

These solutions were kept on the laboratory desk in rubber-stoppered Erlenmeyer flasks, with the exception of No. II, which was kept in the dark. From time to time 10 cc of each of these solutions were evaporated in beakers on the water bath to complete dryness-that is, until the odor of acid had completely disappeared. An examination of the dry residue taken up in the cold with nitric acid wash (50: 1,000) resulted as follows:

TABLE IV. Solubility of residue from 10 cc phosphomolybdic acid solution in nitric acid (50:1,000).

These results show that much depends upon the age of the phosphomolybdic acid solution and upon the method of preparation. ways to be preferred.

Fresh solutions are al

The accuracy of the method proposed for this year was checked by testing chemically pure potassium sulphate, with the result that in a sample containing theoretically 0.1284 gram of potassium monoxid 0.1279 gram was found, and 0.0398 gram was found as compared with 0.0399 gram present according to theory.

The evaporated residue from chemically pure potassium sulphate and phosphomolybdic acid is a fine amorphous powder which gave difficulty in filtering. The addition of a small amount of calcium or magnesium nitrate assisted in the formation of a crystalline residue which facilitated filtering greatly.

The presence of a soluble silica in soil extract did not interfere with the process, except that when the amount was large, filtration became troublesome from the clogging of the filter.

The use of the centrifuge for freeing the yellow precipitate of potassium phosphomolybdate from acid was tried, with good results. The use of a potassium hydroxid solution (1 cc = 1 mg K2O) is probably preferable, but to avoid the labor of preparing two solutions the potassium hydroxid used in volumetric phosphoric acid work was utilized. As a result of all this preliminary work directions were formulated which gave good results in the station laboratory. The samples and directions were sent out as follows:

ASSOCIATION POTASH WORK, 1907.

Sample No. 1.-A sample of soil from the wheat-growing belt of eastern Oregon. This soil contains approximately from 0.25 to 0.5 per cent of acidsoluble potash.

Sample No. 2.-A mixed fertilizer containing considerable quantities of nitrogen, phosphoric acid, and potash (approximately 9 to 10 per cent of potassium monoxid).

WORK ON SOIL.

Mix thoroughly before sampling.

(1) Determine potash (KO) in soil according to the official method using hydrochloric acid, 1.115 sp. gr. (U. S. Dept. Agr., Bureau of Chemistry, Bul. 46 Revised or Bul. 107).

(2) Proposed volumetric method for potash in soils.

Reagents.

Nitric acid.-50.0 cc nitric acid 1.40 sp. gr. in 1,000 cc water.

Sodium nitrate wash.-10.0 grams sodium nitrate per 1,000 cc water. Phosphomolybdic acid solution.-100 grams phosphomolybdic acid (Kahlbaum's preferred) in 750 cc water and 250 cc nitric acid (1.40 sp. gr.). This solution must be freshly prepared-not over three or four days old before using. If properly prepared, the evaporated residue from a portion of this solution is never white and readily redissolves in the dilute nitric acid solution in the cold.

Standard solutions.—Standard caustic potash and nitric acid prepared for volumetric phosphoric acid; 1 cc potassium hydroxid is equal to 1.625 mg K2O,

Determination.

Place a fresh aliquot, representing 1 gram of soil of solution A under soil analysis (Bul. 107 Revised, p. 14), in a tall 200 cc beaker, add 20 cc phosphomolybdic solution, and slowly evaporate to complete dryness on a steam bath. If preferred, use solution without removal of silica, evaporating the acid soil solution directly with phosphomolybdic acid. (It requires approximately 22 mg of phosphomolybdic acid in order to have an excess for each milligram of potassium monoxid present.)

Add 30 cc of nitric acid wash to the dried residue, stir thoroughly in the cold with a grinding motion, using a policeman, allow to settle a moment, and decant supernatant liquid at once through a gooch crucible packed with moist filter-paper pulp approximately one-sixteenth inch in thickness. Wash twice by decantation with sodium nitrate wash, transfer precipitate to gooch, and wash with sodium nitrate wash until acid-free. Transfer gooch to casserole, run in excess of standard alkali solution, and add phenolphthalein. Heat to boiling and titrate excess of alkali with standard acid.

Note. Some samples of asbestos used seemed to hold or "fix" some of the excess acid, making it very hard to wash the gooch filter acid-free. Hence it is suggested to use a paper-pulp filter.

It is suggested that the evaporated residue in the beaker be transferred to a centrifuge tube instead of a gooch, using nitric acid wash, whirl until well settled, decant, and wash with sodium nitrate wash, using the centrifuge, until acid-free. Dissolve in standard alkali and titrate as above.

WORK ON MIXED FERTILIZERS.

Mix thoroughly before sampling.

(1) In sample No. 2 determine water-soluble potash (K2O) by the official method (U. S. Dept. Agr., Bureau of Chemistry Bul. 46 Revised, p. 21, or Bul. 107, p. 11).

(2) Use proposed volumetric method for potash in fertilizers. Transfer 10 cc of solution No. 2 (Bul. 46 Revised, pp. 21-22, or Bul. 107, pp. 11-12) to a platinum dish, and add 0.25 cc of sulphuric acid (1 to 1). Evaporate to dryness and ignite to whiteness. Dissolve residue in hot water plus a few drops of hydrochloric acid and transfer to a tall 200 cc beaker; add 30 cc of phosphomolybdic acid solution and proceed as under proposed volumetric method for potash (K2O) in soils. (If excess of phosphomolybdic acid has been used, the dried residue has a reddish hue. If excess has not been added, the residue is bright yellow. The residue should not appear white.)

In each case run blanks to ascertain corrections to be made for impurities. It is also advisable to treat the potassium-platinic-chlorid residue in the gooch crucible in order to ascertain if it is all soluble in water. Then reweigh the crucible after thoroughly drying.

(See Sut

Note. The caustic potash solution must be free from carbonate. ton, Volumetric Analysis, 9th edition, revised, page 48, for the barium hydrate method, also page 301 for the alcoholic method for making potassium hydroxid free from carbonates.)

A. L. KNISELY, Referee.

B. B. Ross, Associate Referee.

Ten sets of samples were sent out and three reports have been received.

TABLE V.-Comparison of official and proposed volumetric method for the determination of potash in soil and in mixed fertilizers.

M. G. Donk: Could obtain no satisfactory results on sample No. 2 with the volumetric method, presumably due to difficulty in washing yellow precipitate. G. S. Fraps: Sample of phosphomolybdic acid from Merck left considerable white residue, probably molybdic acid, when diluted in nitric acid. This probably accounts for volumetric results being higher than the official method.

C. E. Bradley: Best results were always obtained when using small amounts of potash solution. An aliquot part of a solution of fertilizer containing not more than 0.02 gram K2O gave the best results. If, after evaporating to dryness and taking up in dilute nitric acid, the insoluble residue is not bright yellow, then the conditions are not normal. The washed precipitate should be bright yellow.

COMMENTS BY REFEREE.

It was recommended this year to use a stronger nitric acid wash solution than was formerly used. This was on account of the difficulty experienced in washing the yellow precipitate free from impurities. It has since been ascertained that this difficulty was due to poorly prepared or old phosphomolybdic acid solution. The phosphomolybdic acid solution, when prepared from good, fresh chemicals, should give no blank, and when used in volumetric potash work dissolves and washes out very readily from the evaporated residue. It has recently been found that the nitric acid wash, instead of being stronger than was formerly used, should, if anything, be weaker. In some cases when determining potash in material containing considerable calcium and magnesium and moderate quantities of iron, such as some soil solutions, it is not necessary to use a nitric acid wash solution, but only to dissolve the material at once in the sodium nitrate wash solution.

Official soil solution evaporated to dryness with phosphomolybdic acid and taken up in nitric acid wash gave 0.45 per cent K2O; when taken up directly in sodium nitrate wash the same result was obtained.

I think the merit of the volumetric method for potash depends entirely upon the phosphomolybdic acid solution and the care with which the evaporation is conducted. The difficulties thus far experienced with blanks and in washing the evaporated residues have been largely due to the presence of white insoluble molybdic acid, which at times separates during the process of evaporation and is difficult to remove from the yellow residue of potassium phosphomolybdate.

RECOMMENDATION.

The referee recommends a continuation of the study of the volumetric method for use in both soil and fertilizer analysis; also that the recommendation of Mr. Cushman concerning a study of what really constitutes available potash in soils, fertilizers, and ground-mineral products be continued, so that if possible we may have a definition of available potash.

REPORT ON INSECTICIDES.

By R. J. DAVIDSON, Referee.

The suggestions made in the recommendations of last year were followed as closely as possible, and after consultation with the associate referee the following work was outlined:

(1) Work on London purple to test the Davidson modification of Haywood's method in comparison with the method as originally outlined.

(2) Tests to determine which of the two methods of analysis of soda lye give the more correct results.

(3) Testing the formaldehyde method as modified by Haywood and Smith, in comparison with the method as it originally stood.

(4) Testing the Avery method of determining sulphur in sulphur dips.

(5) Testing the methods of examining lead arsenate as published in last year's proceedings.